feat: v2.1.0 核心重构与功能增强

## 架构重构
- 全局变量消除，迁移至 Config/State 对象
- SMB 插件融合（smb/smb2/smbghost/smbinfo）
- 服务探测重构，实现 Nmap 风格 fallback 机制
- 输出系统重构，TXT 实时刷盘 + 双写机制
- i18n 框架升级至 go-i18n

## 性能优化
- 正则表达式预编译
- 内存优化 map[string]struct{}
- 并发指纹匹配
- SOCKS5 连接复用
- 滑动窗口调度 + 自适应线程池

## 新功能
- Web 管理界面
- 多格式 POC 适配（xray/afrog）
- 增强指纹库（3139条）
- Favicon hash 指纹识别
- 插件选择性编译（Build Tags）
- fscan-lab 靶场环境
- 默认端口扩展（62→133）

## 构建系统
- 添加 no_local tag 支持排除本地插件
- 多版本构建：fscan/fscan-nolocal/fscan-web
- CI 添加 snapshot 模式支持仅测试构建

## Bug 修复
- 修复 120+ 个问题，包括 RDP panic、批量扫描漏报、
  JSON 输出格式、Redis 检测、Context 超时等

## 测试增强
- 单元测试覆盖率 74-100%
- 并发安全测试
- 集成测试（Web/端口/服务/SSH/ICMP）

plugins/services/ftp.go

@@ -0,0 +1,270 @@
+//go:build plugin_ftp || !plugin_selective
+
+package services
+
+import (
+	"context"
+	"fmt"
+	"strings"
+
+	ftplib "github.com/jlaffaye/ftp"
+	"github.com/shadow1ng/fscan/common"
+	"github.com/shadow1ng/fscan/common/i18n"
+	"github.com/shadow1ng/fscan/plugins"
+)
+
+// FTPPlugin FTP扫描插件
+type FTPPlugin struct {
+	plugins.BasePlugin
+}
+
+func NewFTPPlugin() *FTPPlugin {
+	return &FTPPlugin{
+		BasePlugin: plugins.NewBasePlugin("ftp"),
+	}
+}
+
+func (p *FTPPlugin) Scan(ctx context.Context, info *common.HostInfo, config *common.Config, state *common.State) *ScanResult {
+	if config.DisableBrute {
+		return p.identifyService(info, config, state)
+	}
+
+	target := info.Target()
+
+	// 优先检测匿名访问
+	if result := p.testAnonymousAccess(ctx, info, config, state); result != nil && result.Success {
+		return result
+	}
+
+	credentials := GenerateCredentials("ftp", config)
+	if len(credentials) == 0 {
+		return &ScanResult{
+			Success: false,
+			Service: "ftp",
+			Error:   fmt.Errorf("没有可用的测试凭据"),
+		}
+	}
+
+	// 使用公共框架进行并发凭据测试
+	authFn := p.createAuthFunc(info, config, state)
+	testConfig := DefaultConcurrentTestConfig(config)
+
+	result := TestCredentialsConcurrently(ctx, credentials, authFn, "ftp", testConfig)
+
+	if result.Success {
+		// 成功后重新连接获取文件列表
+		fileList := p.getFileListAfterAuth(info, result.Username, result.Password, config, state)
+		var output strings.Builder
+		output.WriteString(fmt.Sprintf("FTP %s %s:%s", target, result.Username, result.Password))
+		if len(fileList) > 0 {
+			for _, file := range fileList {
+				output.WriteString(fmt.Sprintf("\n   [->] %s", file))
+			}
+		}
+		common.LogSuccess(output.String())
+	}
+
+	return result
+}
+
+// createAuthFunc 创建FTP认证函数
+func (p *FTPPlugin) createAuthFunc(info *common.HostInfo, config *common.Config, state *common.State) AuthFunc {
+	return func(ctx context.Context, cred Credential) *AuthResult {
+		return p.doFTPAuth(ctx, info, cred, config, state)
+	}
+}
+
+// doFTPAuth 执行FTP认证
+func (p *FTPPlugin) doFTPAuth(ctx context.Context, info *common.HostInfo, cred Credential, config *common.Config, state *common.State) *AuthResult {
+	target := info.Target()
+
+	conn, err := ftplib.Dial(target, ftplib.DialWithTimeout(config.Timeout))
+	if err != nil {
+		state.IncrementTCPFailedPacketCount()
+		return &AuthResult{
+			Success:   false,
+			ErrorType: classifyFTPErrorType(err),
+			Error:     err,
+		}
+	}
+	state.IncrementTCPSuccessPacketCount()
+
+	err = conn.Login(cred.Username, cred.Password)
+	if err != nil {
+		_ = conn.Quit()
+		return &AuthResult{
+			Success:   false,
+			ErrorType: classifyFTPErrorType(err),
+			Error:     err,
+		}
+	}
+
+	return &AuthResult{
+		Success:   true,
+		Conn:      &ftpConnWrapper{conn},
+		ErrorType: ErrorTypeUnknown,
+		Error:     nil,
+	}
+}
+
+// ftpConnWrapper 包装 ftplib.ServerConn 以实现 io.Closer
+type ftpConnWrapper struct {
+	*ftplib.ServerConn
+}
+
+func (w *ftpConnWrapper) Close() error {
+	return w.Quit()
+}
+
+// classifyFTPErrorType FTP错误分类
+func classifyFTPErrorType(err error) ErrorType {
+	if err == nil {
+		return ErrorTypeUnknown
+	}
+
+	ftpAuthErrors := []string{
+		"530 login incorrect",
+		"530 not logged in",
+		"530 user cannot log in",
+		"530 authentication failed",
+		"authentication failed",
+		"permission denied",
+		"access denied",
+		"invalid credentials",
+		"bad password",
+		"login incorrect",
+	}
+
+	ftpNetworkErrors := append(CommonNetworkErrors,
+		"421 there are too many connections",
+	)
+
+	return ClassifyError(err, ftpAuthErrors, ftpNetworkErrors)
+}
+
+func (p *FTPPlugin) identifyService(info *common.HostInfo, config *common.Config, state *common.State) *ScanResult {
+	target := info.Target()
+
+	conn, err := ftplib.Dial(target, ftplib.DialWithTimeout(config.Timeout))
+	if err != nil {
+		state.IncrementTCPFailedPacketCount()
+		return &ScanResult{
+			Success: false,
+			Service: "ftp",
+			Error:   err,
+		}
+	}
+	state.IncrementTCPSuccessPacketCount()
+	defer func() { _ = conn.Quit() }()
+
+	banner := "FTP"
+	common.LogSuccess(i18n.Tr("ftp_service", target, banner))
+	return &ScanResult{
+		Type:    plugins.ResultTypeService,
+		Success: true,
+		Service: "ftp",
+		Banner:  banner,
+	}
+}
+
+// testAnonymousAccess 测试FTP匿名访问
+func (p *FTPPlugin) testAnonymousAccess(ctx context.Context, info *common.HostInfo, config *common.Config, state *common.State) *ScanResult {
+	target := info.Target()
+
+	anonymousCreds := []Credential{
+		{Username: "anonymous", Password: "anonymous"},
+		{Username: "anonymous", Password: ""},
+		{Username: "ftp", Password: "ftp"},
+	}
+
+	for _, cred := range anonymousCreds {
+		select {
+		case <-ctx.Done():
+			return nil
+		default:
+		}
+
+		result := p.doFTPAuth(ctx, info, cred, config, state)
+		if result.Success && result.Conn != nil {
+			// 获取文件列表
+			ftpConn, ok := result.Conn.(*ftpConnWrapper)
+			if !ok {
+				_ = result.Conn.Close()
+				return nil
+			}
+			fileList := p.listFTPFiles(ftpConn.ServerConn)
+			_ = result.Conn.Close()
+
+			var output strings.Builder
+			output.WriteString(fmt.Sprintf("FTP %s 匿名访问 - %s:%s", target, cred.Username, cred.Password))
+			if len(fileList) > 0 {
+				for _, file := range fileList {
+					output.WriteString(fmt.Sprintf("\n   [->] %s", file))
+				}
+			}
+			common.LogSuccess(output.String())
+
+			return &ScanResult{
+				Type:     plugins.ResultTypeCredential,
+				Success:  true,
+				Service:  "ftp",
+				Username: cred.Username,
+				Password: cred.Password,
+				Banner:   "FTP匿名访问",
+			}
+		}
+	}
+
+	return nil
+}
+
+// getFileListAfterAuth 认证成功后获取文件列表
+func (p *FTPPlugin) getFileListAfterAuth(info *common.HostInfo, username, password string, config *common.Config, state *common.State) []string {
+	target := info.Target()
+
+	conn, err := ftplib.Dial(target, ftplib.DialWithTimeout(config.Timeout))
+	if err != nil {
+		return nil
+	}
+
+	err = conn.Login(username, password)
+	if err != nil {
+		_ = conn.Quit()
+		return nil
+	}
+
+	fileList := p.listFTPFiles(conn)
+	_ = conn.Quit()
+	return fileList
+}
+
+// listFTPFiles 列出FTP文件列表（前6个）
+func (p *FTPPlugin) listFTPFiles(conn *ftplib.ServerConn) []string {
+	files := []string{}
+
+	entries, err := conn.List(".")
+	if err != nil {
+		return files
+	}
+
+	maxFiles := 6
+	for i, entry := range entries {
+		if i >= maxFiles {
+			break
+		}
+
+		fileName := entry.Name
+		if len(fileName) > 50 {
+			fileName = fileName[:50] + "..."
+		}
+		files = append(files, fileName)
+	}
+
+	return files
+}
+
+func init() {
+	RegisterPluginWithPorts("ftp", func() Plugin {
+		return NewFTPPlugin()
+	}, []int{21, 2121, 990})
+}